When conventionally combusting solid phase fuel in industrial burners, a pneumatic system is often used, comprising a carrier gas for conveying the solid phase fuel from an inlet to the place for combustion. For example, the fuel may be in the form of a powder, such as pulverised coal, and may be impelled by the motion of the carrier gas. Frequently, the carrier gas is constituted by air or nitrogen. Such combustion systems may for example be used for heating industrial furnaces.
One problem with such an arrangement is that the carrier gas constitutes a substantial part of the gas flow in the combustion device. Consequently, large amounts of ballast gas, for example in the form of nitrogen, must be heated, which leads to deteriorated efficiency.
Furthermore, it would be desirable to use solid phase fuels together with oxyfuel combustion devices, in other words such devices where the oxidant has a large oxygen concentration. One problem with such combustion is that flame temperatures locally become very elevated. In combination with the large amounts of nitrogen present in the combustion zone, this results in elevated levels of NOx in the combustion gases, something which is not desirable because of, among other things, regulatory and environmental concerns. At the same time, it has proven to be very difficult to adapt a conventional combustion device for solid phase fuel so that dilution of the fuel with furnace gases can take place, for the purpose of achieving a so called flameless combustion, that is combustion with such a diffuse combustion zone so that a visible flame is essentially absent, and thereby achieving lower combustion temperatures.
Thus, it would be desirable to achieve a way to efficiently combust solid phase fuel the combustion products of which contains low levels of NOx.